Western US's Stronger Storms Traced to Asia Pollution ; Winter Cyclones May Be Gaining Intensity as They Pick Up Soot and Other Particles, Says a US Research Team

Article excerpt

Air pollution blowing over the western US from Asia has been a growing environmental concern for several years. Now, it seems, it's giving winter storms added punch as well.

Tiny aerosols and soot from burning wood and coal in winter, especially in China, appear to be seeding clouds in large winter storms that churn thousands of miles east across the northern Pacific, says a team of US scientists. The pollution is turning relatively routine marine rain clouds into towering thunderheads, much like those seen above land.

Previous studies have shown that during the last half of the 20th century, northern Pacific winter storms have become steadily more frequent and stronger, based on tracking wind speeds and atmospheric pressure. The latest results, published last week, indicate that ill winds blowing out of Asia are adding muscle to the types of clouds these stronger winter cyclones carry.

The team posits that the shift toward these types of clouds, with their strong updrafts, could be altering global circulation patterns - perhaps even masking the effects of global warming, because the thicker, taller clouds reflect more sunlight back into space. And they could be contributing to more rapid melting of snow and ice in the Arctic as dark soot is lofted by strong updrafts in these clouds and carried north to fall back to the surface.

Others have noted this effect of smoke and soot on individual thunderstorms in the Amazon. But this is the first time researchers have seen the effect on storm systems hundreds of miles across.

"As you change things in the atmosphere, whether it's particulates or climate change, all of the effects are not obvious" immediately, says Renyi Zhang, an atmospheric scientist at Texas A&M University in College Station, who led the study.

A poor grasp on aerosols' effects

The team has long been interested in the effects soot and tiny particles called aerosols have on climate. The latest report on global-warming science from the Intergovernmental Panel on Climate Change, released last month, shows that researchers have a poor grasp on these effects. Of all the agents affecting climate - sunlight, greenhouse gases, mineral dust blowing around, for example - the "indirect" effect aerosols have on climate through seeding clouds remains the largest source of uncertainty the report lists. …

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